Place the chicken bones on a tray together with the chicken necks. Now toast the bones and necks at 180 °C (356 °F) for 45 minutes.
Meanwhile cut the onion in half and clean it. Now slice it in thin slices. You’ll need 150 grams. Then cut the top part of the leek in half and wash it well under cold water. Slice it as well and do the same with the celeriac and the celery. Also cut the garlic in half.
Once you’re happy with the color of the chicken you can transfer it into a big pan and deglaze the oven tray with the white wine. Let it soak for 10 minutes in the oven.Â
Now submerge the chicken with cold water and also add the white wine from the oven tray. Then add the cut vegetables with the thyme, the bay leaves, the black pepper and the coriander seeds.
Bring this to a simmer and let it simmer for at least 6 hours. If needed add some more water in between. Once you’re happy with the flavor pass the broth through a fine sieve and let it drip for at least 30 minutes so you don’t waste a single drop.
After that let the broth reduce for around 80% and while it’s reducing remove any fat or protein that’s floating on top. Clean the ladle in between to get the best result and once all the fat is removed set 250 grams of the broth aside for later. We need it for the bitterballen.
While the broth is reducing you can also reduce the madeira for around 80% till it has a sticky syrup consistency.
Once you’re happy with the flavor of the broth pass it through a fine sieve once more.Â
Now add a drizzle of the reduced madeira to the reduced chicken sauce and keep on tasting and adding reduced Madeira till you're happy with the flavor. When you think the flavor is too powerful add a drizzle of sherry vinegar or champagne vinegar.
Then you can keep the sauce covered in your fridge for later.Â
